It is known that telephone lines and similar communication lines require protection from over voltage and excess-current conditions caused by power surges, lightning and similar undesired conditions. It is also known that hermetically sealed cold cathode gas tubes are a preferred form of primary arc gap arrester structures which, as is well known, includes a pair of electrodes spaced by an insulator and hermetically sealed to form the arc gap. Also, it is known that failure of cold cathode gas tubes is not unknown and that detection of such failure is most difficult since the electrical circuitry connected thereto operates normally and is only affected when excess or undesired conditions are encountered. Thus, provision of one or more "back-up" or redundant systems appears prudent.
One known attempt to provide added protection in a surge arrester assembly is set forth in U.S. Pat. No. 3,755,715, issued Aug. 28, 1973. Therein, a plurality of cup-like structures and a perforated insulator device are employed to provide a secondary arc gap having a break over voltage greater than the break over voltage of a cold cathode gas tube. Moreover, a solder pellet is also disposed within one of the cup-like structures to provide added protection against excessive voltage or current over an extended period of time. Unfortunately, the above-described structure leaves something to be desired due to the use of numerous non-standard parts which are not only difficult to obtain but also costly as well.
Attempts to overcome some of the difficulties of the above-described assembly are set forth in U.S. Pat. Nos. 4,208,694 and 4,241,374, issued June 17, 1980 and Dec. 23, 1980 respectively. Therein, a solder pellet is located intermediate first and second metal cups. The first metal cup engages one electrode of a gas discharge tube and has resilient fingers which contact an off-set portion of the second metal cup. The resilient fingers force the off-set portion of the second metal cup against an insulator ring and a secondary arc gap is provided intermediate the off-set portion of the second metal cup and an electrode of the arc discharge tube. Additionally, an O-ring and sealing compound are utilized in an attempt to protect the secondary arc gap from undesired ambient contaminants.
Although the above-described assemblies have provided enhanced capabilities, it has been found that there is still much to be desired insofar as improved over voltage protection and uniformity of result is concerned. Also, an assembly which utilizes sealing compounds to provide an assembled structure is most difficult to assemble without encountering undesired handling difficulties.
Still another known attempt to overcome the difficulties of the previously described structures is set forth in an application bearing U.S. Ser. No. 433,498, filed Oct. 8, 1982. Therein, a cage member with resilient fingers is slideably positioned within a housing member and includes a cold cathode gas tube providing a primary arc gap and an insulator having a plurality of holes and disposed intermediate a gas tube electrode and an electrical conductor to provide a secondary arc gap. The electrical conductor is held in position by the resilient fingers of the cage member.
Although a great improvement over previous known structures, problems were encountered in assembly fabrication and cost. For example, it was found that relying on the resilience of the fingers to retain structural integrity leaves something to be desired. Also, a multiplicity of components which require manufacturing operations adds to the cost of the structure. Further, it was found that direct contact of the solder pellet and a relatively large metal structure tends to undesirably develop a "heat sink" condition which is deleterious to the desired operation of the assembly.